It is known that pipe systems of analytical apparatus such as liquid chromatography apparatus or a mass spectograph and pipe systems (for transporting a processing liquid) of a semi-conductor manufacturing machine is heated by means of a flexible heating sheet.
Heretofore, a flexible heating sheet composed of two heat resistant films and an electric heating element such as a nichrom wire and a stainless steel wire intervening between the heat resistant films. The electric element has an electric source-connecting terminal at each end. The heat resitant film is a glass cloth or a silicone resin film. The glass cloth has poor insulating property. The silicone resin film should be formed to have an enough thickness such as 1 mm thick or more. Moreover, the silicone resin film is heat resistant only up to 200° C.
JP2001-15254 A describes a flexible heating sheet comprising an electric heating element covered with a heat resistant aromatic polyimide film on both sides. The electric heating element is sandwitched between the heat resistant aromatic polyimide film via an adhesive layer.
It is an object of the present invention to provide a flexible heating sheet having improved heat resistance so that the flexible heating sheet can be employed under conditions invoving elevated temperatures.